Cholesterol cholelithiasis is a common disease, affecting 10-20% of the population between the ages of 55 and 64. The deaths and disability due to this disease and the costs of treatment have prompted intensive research into the etiology, prophylaxis, and non-surgical treatment of cholesterol gallstones. The evidence indicates that a prereqiusite of cholesterol gallstone formation is the production of hepatic bile which contains an increased ratio of cholesterol to bile salts and lecithin. The bile acids have a major influence on the secretion of cholesterol and lecithin. Our study will examine in detail and compare the efficiency of hepatic excretion of each of the three major human bile salts: cholate, chenodeoxycholate, and deoxycholate, and determine the influence of each on biliary cholesterol, phospholipid and water excretion in bile-fistula rats. Specifically the following questions will be studied: 1) Is there any competition for hepatic excretion among these bile salts? An experiment using intravenously infused radioactive bile salts will be directed at this question. 2) Is lecithin excretion limited at high chenodeoxycholate and deoxycholate excretion rates as has been observed for taurocholate? 3) What are the mechanisms for limitation of biliary lecithin at high bile salt excretion rates? We will study the influence of intravenous infusion of lecithin precursors and of dietary lecithin, also measure hepatic and microsomal content of palmityl-linoleoyl-lecithin to answer this. 4) Is the lecithin-dependent cholesterol excretion rate changed by infusion of different bile salts? 5) What influence does each bile salt have on the bile salt independent fraction of bile flow? 6) What are the effects of age on some of these parameters? 7) Does essential fatty acid deficiency alter some of the parameters under study? The results of this study will be of help in further clarification of the role of the bile acids in etiology and in the development of adjuvant therapy of cholesterol gallstones and in forming a basis for future human studies.